# Explain how the structure of a DNA nucleotide differs from that of an RNA nucleotide, and how these structural differences affect the chemical stability of each type of nucleic acid.

> IB DP Biology Higher Level (2023 syllabus) — A1.2 Nucleic acids · Explain · 4 marks

## Mark scheme (4 marks)

1. DNA nucleotides contain deoxyribose (lacking a hydroxyl group at the 2' carbon), whereas RNA nucleotides contain ribose (with a 2'-OH group).
2. DNA nucleotides contain the base thymine, whereas RNA nucleotides contain uracil in its place; both pair with adenine.
3. The 2'-OH group in ribose makes RNA more susceptible to hydrolysis / alkaline cleavage, because it can act as an intramolecular nucleophile attacking the adjacent phosphodiester bond.
4. The greater chemical stability of DNA (due to deoxyribose and the double-stranded helix) makes it better suited to long-term storage of genetic information, whereas the relative instability of RNA is acceptable given its transient functional roles.

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